1. Field of the Invention
The present invention relates to a method for restraining deformation of a nip roll used in a size press process of a paper-making machine or in other applications.
2. Description of the Related Art
For example, in the size press process of paper-making machine, paper is pressed by two nip rolls that are brought into contact with each other by pressure.
In the paper-making machine industry, there is a tendency toward high speed. However, the nip roll shows a tendency to vibrate especially at the time of high-speed rotation, which causes a hindrance to high-speed rotation.
This vibration is ascribed to a phenomenon that the same portion of each roll is strongly nipped because of the relationship between the rotational speed of each roll and the natural frequency of a vibration system including the rolls, supporting means therefor, and the like, whereby the roll is deformed into a polygonal shape. Conventionally, since the diameter ratio between nip rolls is set at 1, the same portions thereof are nipped strongly, so that large vibration occurs due to the deformation into the polygonal shape.
As measures against the deformation of nip roll, an increase in roll diameter can be thought of. If the roll diameter is increased, the rotational speed of the roll can be decreased by the amount of increase in the circumferential speed of roll. If the rotational speed decreases, time for restoring the deformation of roll is secured, so that the growth of deformation is restrained. However, such measures increase the size of roll, which leads to the increase in roll cost and installation space.